U.S. Pat. No. 4,057,204 issued Nov. 9, 1977 in the name of R. E. Zajac to Windings, Inc. ("Zajac") discloses a payout tube of the above described sort in which an annular flange encircles the tube near its exit end to provide a planar stop surface extending continuously around the tube and the tube has at such end, outward of the flange, on diametrically opposite sides of the tube, a pair of projections which extend radially out from the tube to lie over the flange and which are shown as being of triangular cross section in planes normal to the radial center lines of the projections. The walls of such projections towards that flange are planar and slope in opposite directions as seen in a direction along the tube diameter between those center-lines.
The Zajac tube is secured in position within the container by (a) providing in a wall of the container a circular hole of the tube's diameter and having equiangularly spaced around it a pair of notches formed in the hole's circumference for receiving the tube projections, (b) positioning the tube inside the container to pass a stub portion of such tube through such hole and such projections from inside to outside through such notches until the tube flange bears against such wall around the circumferential margin of the hole, and (c) then turning the tube 90.degree. to cause portions of the wall around the tube to be interposed between such flange and the two projections to thereby secure the tube to the wall. According to the Zajac patent as it is understood, what happens in the course of such turning is that, because the space between the flanges and the axially inner edges of the sloping projection walls towards the flange is a space less than the wall thickness of the container, the turning of the tube causes the inclined lower surfaces of the projections to ride up on the box material and grip into it to prevent accidental turning of the tube to an improper position. The Zajac patent also indicates in its abstract that improper turning of the tube is avoided because the effect of the tube projections on the box material is that the projections "dig into it".
The Zajac Tube is shown as having a cylindrical outer surface and a coaxial circular cylindrical inner surface circumferentially extending around and bounding a cylindrical bore formed in the tube and through which the cable or other filament is led. The end surface of the tube at its entrance and is a planar annular surface meeting the two mentioned cylindrical surfaces at respective circular edges which are at the radially inner and outer margins of that annular surface, and which edges are sharp. Accordingly, the Zajac tube at its entrance end has very little or nothing to inhibit the formation in cable being led through the tube of kinks and angular bends in the cable in the event the cable has to follow a curved path in the course of moving from the coil into the tube.
U.S. patent application Ser. No. 07/572812, filed Aug. 24, 1990 for "Payout Tube for Container Packaged Coiled Filament" in the name of Rodney J. Hunt, now U.S. Pat. No. 5,064,136, and assigned to the assignee hereof, and incorporated herein by reference and made a part hereof ("Hunt"), discloses a payout tube which is deemed to be an improvement over the Zajac tube in a number of respects. One of these is that the entrance end surface of the Hunt tube is shown as being a convex surface which substantially conforms to a hemi-toroidal surface produced by bisecting a torus in its center plane, and which end surface has a faired joinder at its radially inner and outer margins with the inner and outer surfaces of the tube. That rounded end surface of the Hunt tube tends to impose on the radius of curvature of bends formed in the cable in entering the tube a lower limit for such radius equal to the radius of curvature of the hemi-toroidal end surface. A difficulty, however, is that such radiis of curvature for such end surface is too small to prevent damaging bending of certain codes of cable.
As a specific example, it was desired to dispense from a box container of the sort described a quantity of a particular cable. To the end of determining if such dispensing could be satisfactorily done, a coil of such cable was placed in such a container to evaluate how well it could be pulled from the box through a Hunt tube having the rounded entrance end surface described above. It was found that the traversed layers of the cable next to the tube could not easily make the reverse bend to enter the tube without kinking the cable and sometimes tearing the jacket when sufficient force was applied to pull the cable through the tube.